380 



WILLIAM L. DOLLEY, JR. 



between the rays of light and the trail of the insect at the edge 

 of the beam in each of the trials was measured. This anglejs 

 termed the 'angle of deflection.' The average then was com- 

 puted for a number of the first trials on each day, this number 

 being equal to the number of trials on that day on which fewest 

 trials were given. The columns marked Tlace where orientation 



Fig. 6 Reproduction of 40 trails made by butterfly 10/1-b (left eye blackened) . 

 A, 1-20, trails made in successive trials on the first day of the tests; B, 1-20, trails 

 made on the second day of the tests; a and b, limits of horizontal beam of light; 

 small arrows, direction of movement of animal; large arrows, direction of rays 

 of light; illumination at x, 925 mc; at y, 266 mc. Note that this insect modified 

 its reactions in that it made numerous circus movements in the trials on the 

 first day, bij,t made none in the trials on the second day. 



occurred' also demand some explanation. By 'Orientation' is 

 meant the assumption of an axial position with the head pointed 

 directly toward the glower followed by movement in this direc- 

 tion. If the animal turned and moved directly toward the source 

 of light before it reached the edge of the beam it is said to have 

 oriented 'in the beam.' If it, however, went more than one centi- 

 meter beyond the edge before it turned toward the glower it is 



